It is generally known to use magnetic resonance (MR) imaging and spectroscopy for investigating laboratory animals, in particular laboratory rodents, e.g. mice. For MR investigations, the mouse is to be arranged in the magnet bore of an MRT device in an immovable manner. For this purpose, animal holding devices are used, which are adapted for a fixation of the animal in the magnet bore.
FIG. 11 schematically illustrates a conventional prior art animal holding device 100′ as it is practically known for laboratory investigations of mice. The animal holding device 100′ comprises an carrier platform 310′, which is arranged in the magnet bore 210′ of an MRT device 200′. The carrier platform 310′ is connected and movable with a rail system 250′ of the MRT device 200′. The carrier platform 310′ accommodates an HF head coil 230′ and the mouse 1, which is fixated with a conical receptacle 311′ and ear pins 314′. Narcosis gas is flowed to the mouse 1 through the conical receptacle 311′. The HF head coil 230′ is arranged above the head 2 of mouse 1. Adjacent to the carrier platform 310′, an HF receiver and/or transmitter coil (resonator coil) 240′ is arranged.
The conventional animal holding device 100′ has a series of disadvantages in terms of conditioning the mouse 1 and providing stable and reproducible measurement conditions. In particular, the disadvantages can be summarized as follows. Firstly, the carrier platform 310′ is hanging in a suspended manner. Due to switching of strong magnetic field created in the MRT device 200′, mechanical forces can be caused, which result in vibrations or other irregular movements of the carrier platform 310′. These movements essentially impair the MR imaging. As a further disadvantage, the conical receptacle 311′ represents a limitation for a close and reproducible positioning of the HF head coil 230′ to the mouse head. This disadvantage is even increased with the investigation of small groups of laboratory animals as it is the case e.g. with mice having gene manipulations. While variations of the face and head shapes can be simply compensated by statistical methods with mass investigations of large animal groups, this is impossible with small animal groups. In this case, the HF head coil 230′ is to be positioned as close as possible to the mouse head for avoiding influences by the above shape variations.
Furthermore, the conical receptacle 311′ does not allow a controlled breathing of the mouse by so-called positive pressure breathing as the receptacle 311′ cannot be sealed relative to the mouse head. Accordingly, a positive breathing pressure can not be provided with the conventional animal holding device 100′. Finally, the conventionally used rail system 250′ represents a disadvantage in terms of low lateral stability and lack of longitudinal adjustment along the magnet bore 210′. Again, this disadvantage deteriorates the MR imaging quality.
Another disadvantage is given by the fact that the conventional structure does not allow an easy interchangeability of the animal holding device by another holding device accommodating e.g. an MR phantom for reference measurements. The conventional animal holding device represents a special tool exclusively for holding animals. It is not suitable for holding other non-living test-subjects, like a sample container.
Another disadvantage of conventional MRT devices is related to the positioning of the resonator coil 240′ in the magnet bore 210′. With conventional practice, the resonator coil 240′ is positioned with one of the following techniques. Firstly, the resonator coil can be supported with a construction of radially extending plates connected with axially connected rods. The radially extending plates are fixed in the magnet bore with screws. As the main disadvantage, these screws can be handled only near the opening of the magnet bore. Generally, a resonator coil cannot be stably fixated in an inner part of the magnet bore.
According to a second technique, one of the radially extending plates is replaced by a ring-shaped air-filled hose. The hose can be supplied with pressured air at the positioning site within the magnet bore. However, due to the elasticity of the hose, a stable positioning of the resonator coil is not possible. This disadvantage is even increased during the operation of the MRT device, when the inner volume of the magnetic bore is heated or cooled down.